The general background of the invention is that a laser rod is pumped by any energy source, the rod being provided with end mirrors one of which is a total reflector and the other is a partial or semi-transparent reflector, switching means being provided for short-pulse lasers such as in range finding, these being in the nature of a shutter and being interposed between one of the mirrors and the amplifying rod of the laser, the general principle being that the rod is excited beyond the degree ordinarily needed for laser action, but the shutter prevents such action. When the shutter is abruptly opened, the stored energy is released in a large pulse of short duration.
One of the methods which has been used heretofore to give this shutter action has been to use a spinning prism having its axis of rotation at right angles to the axis of the rod but having its optical axis coaxial with the rod, so that when this prism is spun, there is only one short period during the rotation of the prism when the prism acts as a back reflecting mirror, thus causing the prism to act as a shutter to allow the laser to be pumped prior to the commencement of lasing.
In the simple type of Q-switching the ray passes twice through the rod because the prism is coaxial with the rod, and it has been found in practice that this causes a loss of efficiency due to the second amplification effect, and to try and avoid this an earlier system utilizes a single rotating switching mirror between the ends of the laser rod and the totally reflective mirror but such a mirror then must be placed remotely of the axis of the laser rod with consequent increase in dimension of the unit and problems in mounting and correct orientation of both the reflective mirror and the rotating mirror.
Another system also envisaged was to have a remote mirror placed with its face parallel to the partially reflective mirror but outside of the plane of the laser rod itself and to then use a pair of oppositely rotating mirrors, one in the plane of the laser rod and the other positioned to direct the ray from the first mirror to the totally reflective mirror. Here while some space may be saved, again certain problems exist in mounting and maintaining alignment although an increase in efficiency can be expected.